Photometric analysis of the blood gas parameters pH, oxygen (O.sub.2) and carbon dioxide (CO.sub.2) is in itself prior art, which is described in detail in a large number of publications. A representative selection of these publications is listed below.
Photometric determination of the oxygen concentration in blood or other media by the so-called luminescence quenching is thus known from i.e.,
Bacon, J. R. and Demas, J. N., "Determination of oxygen concentrations by luminescence quenching of a polymer immobilized transition-metal complex", Anal. Chem., 59, 1987, 2780-2785, PA0 Longmuir, I. S. and Knopp, J. A., "Measurement of tissue oxygen with a fluorescent probe", Journal of applied physiology, 41, 1976, 598-602, PA0 Waughan, W. M. and Weber, G., "Oxygen quenching of pyrenebutyric acid fluorescence in water. A dynamic probe of the microenvironment", Biochemistry, 9 (3), 1970, 464-473, PA0 Bergman, I., Nature 218, 1958, 376, PA0 Stevens in the specification of U.S. Pat. No. 3,612,866, PA0 Stanley in the specification of U.S. Pat. No. 3,725,658, PA0 Bacon, J. R. and Demas, J. N. in the specification of British patent application GB 2132348, PA0 Peterson et al. in the specification of U.S. Pat. No. 4,476,870, PA0 Buckles, R. G. in the specification of U.S. Pat. No. 4,399,099, PA0 Hirschfeld, T. in the specification of U.S. Pat. No. 4,542,987, PA0 Dukes et al., in the specification of U.S. Pat. No. 4,716,363, PA0 Lubbers et al. in the specification of U.S. Pat. No. Re. 31,879, PA0 Kahil et al. in the specification of International patent application WO 87/0023, PA0 Murray, R. C., Jr. and Lefkowitz, S. M. in the specification of European patent application EP 190829, PA0 Murray, R. C., Jr. and Lefkowitz, S. M. in the specification of European patent application EP 190830, and PA0 Hesse, H. C. in the specification of East German patent DD 106086. PA0 Manuccia et al. in the specification of U.S. Pat. No. 4,509,522, PA0 Mosse, C. A. and Hillson, P. J. in the specification of British patent application GB 2160646, and PA0 Nestor, J. R. in the specification of European patent application EP 253559. PA0 Seitz, W. R. and Zhujun, Z. in the specification of U.S. Pat. No. 4,548,907, PA0 Wolfbeis, O. S. et al., "Fluorimetric analysis. 1. A study of fluorescent indicators for measuring near neutral ("physiological") pH-values", Fresenius Z. Anal. Chem. 1983, 314, 119-124, PA0 Peterson, J. I. et al., "Fiber optic pH probe for physiological use", Anal. Chem. 1980, 52, 864-869, PA0 Kirkbright, G. F. et al., "Fiber optic pH probe based on the use of an immobilized colorimetric indicator", Analyst 109, 1984, 1025-1026, and PA0 Gerich I. L. et al., "Optical fluorescence and its application to an intravascular blood gas monitoring system", IEEE Transactions on Biomedical Engineering 2, 1986, 117-132.
Determination of the carbon dioxide content in blood by irradiating with 4,26 .mu.m radiation is known from:
Determination of pH in blood by contact with a pH indicator is known from, i.e., the following publications:
Determination of the intraarterial values of all three blood gas parameters by means of a fluorescence based measuring system is known from Miller et al,. "Performance of an in-vivo, continuous blood-gas monitor with disposable probe", Clin. Chem. 33 (9), 1987, 1538-1542. Extracorporeal determination of all three parameters by means of an also fluorescence based measuring system Gas-STAT.TM., produced by Cardiovascular Devices Inc., USA, is finally described in brochures concerning this system and in the article by Clark, C. L., "Early clinical experience with Gas-STAT", J. Extracorporeal Technol., 18 (3), 1986, 185-189. The determination of the blood gas parameters proceeds continuously in the Gas-STAT.TM. system. Inside a cuvette, which is inserted in the extracorporeal circulation established at a cardiac operation, fluorescence based sensors are placed. Via optical fibers excitation radiation is provided and emitted fluorescence radiation is taken away. The intensity of the latter depends of the concentration of the matter measured by the relevant sensor.
None of these publications relating to photometric analysis of the blood gas parameters describes an in vitro method for determination of one or several blood gas parameters in discrete samples and based on simple sample handling principles.
However, in vitro determination of the blood gas parameters pH, oxygen, and carbon dioxide in a blood sample has so far mostly been performed by means of blood gas analyzers as, e.g. the blood gas analyzers produced and sold by Radiometer A/S, Copenhagen, under the name ABL Acid-Base Laboratory.
These analyzers are mechanically complex, since the blood samples i.a. have to pass through the very fine fluid conduits of the analyzer, in which conduits electrochemical sensors are built-in. Blockage in the conduits or coatings on the active surfaces of the sensors can easily occur and interfere in or destroy a measurement.
On account of these circumstances the existing equipment requires frequent maintainance performed by specially trained personnel, and the equipment will normally be placed in a laboratory situated at a certain distance from the patient. A period of reply of more than 10 min. and normally up to half an hour from the time of the sampling to the moment of the analysis result being present is therefore not unusual. Beyond that the waiting period can be unfortunate in connection with the medical treatment of the patient, the relatively long waiting period also has the consequence that the sample is to be kept cooled down to app. 0.degree. C. This is due to the fact that at higher temperatures the metabolic processes of the blood will cause changes in the blood gas parameters during the relevant periods.
Another disadvantage of the existing equipment is that there exists a certain risk for the operator to get in touch with sample residue with the health risks this may imply in the form of transfer of infections, etc.